Theoretically, if PS3 components became magically dirt cheap...
Nintendo would be fine. They'd still sell to many of the same customers, many of whom don't even consider the HD console route an option. They wouldn't cut price just for marketshare, I highly doubt they care about it (and rightly so, they carry the system on their own). The Wii would probably continue to outsell the PS3 once the price cut craze wears off.
MS would be doing worse, but it's not as if those prices would drop 360 sales to zero. The 360 is a fine deal, regardless of how the PS3 is priced (though anyone that doesn't care for 360 exclusives will pass on it). Even if their sales dropped to 35-50% of their current sales, they already have an enourmous install base who will continue to buy software.
